The present invention relates to disc recorders and more specifically to recorders to which video information is recorded on a rapidly rotating magnetic disc. The disc used in such a recorder may be constructed of either rigid or flexible material. The recording disc is rapidly rotated and one or more transducer heads are positioned adjacent the recording surface. If desired, transducers may be provided for recording and playback on both sides of the recording disc.
Recording of video signals on a disc recorder may be accomplished in a number of ways. In one format, the signal is stored in a number of circular concentric recording tracks. The tranducer is moved only intermittently to the desired track for recording or playback. Generally one field of video information will be stored in each of the tracks. The disc will be rotated, therefore, at a rate equivalent to the field rate of the video signal. As can be readily appreciated, the motion of such transducer heads between tracks must be very rapid if all of the fields in a video signal are to be recorded, since 60 fields per second are present in the standard television signal in use in the United States.
One prior art transducer drive arrangement is shown in U.S. Pat. No. 3,539,716, issued Nov. 10, 1970, to Stratton et al. In the Stratton et al device, four transducer heads are positioned adjacent tracks defined on both sides of two rigid magnetic discs. These transducers are mounted on relatively heavy head carriages which encircle and are slidable on generally radially positioned arms. Each head carriage is attached to metal belts which engage a drive pulley and an idler pulley at opposite ends of the arm. The drive pulley may be rotated by a stepper motor to cause the head carriage to slide to predetermined positions along the arm.
The rigid disc type of recorder shown in the Stratton et al patent is not tolerant of transducer head position variations and, therefore, the head carriage must be positively and securely attached to the arm. The transducer carriage configuration utilized, while providing dimensional stability, requires a relatively long period of time to move between tracks due to its mass. The time required for a transducer to move between adjacent tracks is slightly less than one-fifth of the time interval corresponding to a field of video information. The Strattton et al device, however, compensates for the slow stepping mechanism by using four separate transducer heads which are sequentially actuated and transported.
A second type of prior art transducer transport is shown in U.S. Pat. No. 3,770,905 to Sperry, issued Nov. 6, 1973, and U.S. Pat. No. 3,814,441 to Craggs, issued June 4, 1974. These patents show transport mechanisms in which a radially disposed threaded rod is engaged by the transducer carriage. Rotation of the rod by a stepping motor causes the carriage to move to a desired position. Since the carriage mechanism and the threaded rod it engages are both moving in such a device, the inertia of the transport is significant and rapid stepping motion is difficult to obtain.
A second recording format for disc recorders is shown in U.S. Pat. No. 3,509,274, to Kihara, issued on Apr. 28, 1970. The transducer head is moved radially during disc rotation such that a continuous spiral track is defined. While such a recording format permits a slower transport mechanism to be utilized, this format is disadvantageous in that continuous high quality reproduction of a single video field, or series of fields, is not easily obtained.